ARC Ref and tube rolling

I am a newbie when it comes to tube equipment. I have had the ARC Ref 3, Ref 110, and Ref CD7 for a couple of years and they are my first set of tube components. Has anyone experimented with tube rolling with any of these units (what are some of the favorite flavors of the 6550 output tubes in the Ref 110 - which I guess is the obvious place to tube roll - relative to the stock tubes that come from Audio Research)? Also, are there any issues one ought to look out for if one were to experiment with tube rolling with ARC components (voided warranties, ARC gear not self biasing, etc...)? Thx for help in advance.